Abstract: In view of problems of high switching loss, serious interphase interference and low DC side voltage utilization in tracking compensation current and voltage of traditional mine-used unified power quality conditioner, a constant frequency double hysteresis control strategy based on space voltage vector was proposed. Through the tracking analysis of single-phase current and voltage hysteresis loop, the function relation between the width of time delay loop with fixed switching frequency and the voltage on the grid side is obtained. Then, the width of double hysteresis loop is dynamically adjusted according to change of the grid-side voltage to ensure the constant switching frequency, which can effectively reduce switching loss while tracking compensation current and voltage. Combination of constant frequency double hysteresis loop control and space voltage vector can eliminate phase interference and improve voltage utilization rate, and can reduce current harmonics while ensuring current response speed. The simulation results show that the power quality conditioner adopting this control strategy can compensate grid voltage and current in time and effectively when voltage sag and current waveform are distorted, and the harmonic distortion rate of voltage and current after compensation is low, which ensures safe operation of coal mine power grid.